This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 2002-0026924 filed in Korea on May 15, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a cathode ray tube, and in particular to a funnel structure for a cathode ray tube which is capable of preventing breakage by stress concentration.
2. Description of the Prior Art
In general, a cathode ray tube materializes an optical screen by converting an electric signal into an electron beam and emitting the electron beam onto a fluorescent surface. Because the cathode ray tube has excellent display quality in contradiction to a price, it is widely used.
The cathode ray tube will be described in detail with reference to accompanying drawings.
FIG. 1 is a longitudinal-sectional view illustrating a general cathode ray tube.
In the general cathode ray tube, a front glass as a panel 1 is combined with a rear glass as a funnel 5, and it is sealed in a high vacuum state.
And, the cathode ray tube includes a fluorescent surface 3 coated onto the internal surface of the panel 1 and performing a certain luminescent material function; an electron gun 13 emitting an electron beam 14 for making the fluorescent surface 3 fluoresce; a deflection yoke 10 installed at the outer circumference of the funnel 5 and deflecting the electron beam 14 so as to be scanned appropriate to an area of the fluorescent surface 3; a shadow mask 6 installed with a distance from the fluorescent surface 3; and a reinforcing band 15 installed at the side circumference of the panel 1 and dispersing stress occurred on the panel 1 and the funnel 5.
The panel 1 has a curved inner surface and a substantially flat outer surface.
The funnel 5 performs a vacuous body function with a certain space formed by being combined with the panel 1 and the electron gun 13 and fixedly supports the deflection yoke 10 and the electron gun 13.
The funnel 5 is largely divided into a body portion 51 at which the panel 1 is installed, a yoke portion 52 at which the deflection yoke 10 is installed and a neck portion 53 at which the electron gun 13 is installed.
Herein, a line of demarcation between the body portion 51 and the yoke portion 52 is called a TOR (top of round) 7, a line of demarcation between the yoke portion 52 and the neck portion 53 is called a neck seal 9, and an imaginary line as a base of the total length of the funnel 5 is called a reference line 8.
In addition, a portion at which the panel 1 and the funnel 5 are combined with each other is called a sealing surface 4, twice of an angle 18 of a cross point between a center axis 12 of the funnel 1 and the reference line 8 to an imaginary line connecting the cross point with an effective surface end 17 of the shadow mask 6 is called a deflection angle.
In the above-described cathode ray tube, because the cathode ray tube has a large width comparably, it is difficult to secure an installation space, in addition, it is heavy. In more detail, with a recent slim-lightweight trend in electronic equipment, in order to slim down the cathode ray tube, a method of reducing the total length of the panel 1 and a method of reducing the total length of the funnel 5 can be used.
Herein, when the total length of the panel 1 is reduced, by vacuuming after an exhaust process, high tensile stress is occurred on the sealing surface 4 at which the panel 1 and the funnel 5 are combined with each other. In addition, because a space for combining the reinforcing band 15 is reduced, stress dispersion efficiency of the reinforcing band 15 is lowered.
In the meantime, when the total length of the funnel 5 is reduced, relatively high stress occurs on the funnel 5 having a thickness smaller than that of the panel 1. In particular, because high tensile stress occurs on the sealing surface 4 at which the panel 1 and the funnel 5 are combined with each other, breakage may easily occur in production process.
Therefore, tensile stress in vacuum has to be thoroughly considered, in general, a limit stress value of the funnel 5 is not greater than 12 MPa in designing. In more detail, when stress value of the funnel 5 is not less than 12 MPa, a crack may occur even in a small impact, the stress may proceed the crack, and accordingly implosion of the funnel 5 may occur.
In the meantime, in order to reduce the stress concentration, a thickness of the body portion 51 of the funnel 5 can be increased, in that case, a thickness difference between the yoke portion 52 and the body portion 51 is increased, in a temperature lowering process in fabrication of the funnel 5, a crack may occur by a heat capacity difference due to the thickness difference between the body portion 51 and the yoke portion 52.
In addition, when the thickness of the yoke portion 52 is increased inwardly, a BSN (beam shadow neck) in which the electron beam 14 is covered by interference of the internal surface of the yoke portion 52 occurs, a screen quality of the cathode ray tube is lowered.
Therefore, in lowering the stress concentration according to the sliming-down of the funnel 5, the method of increasing the thickness of the funnel 5 is not preferable. Instead, it is most preferable to use a method of optimizing a shape of the funnel 5.
Accordingly, in order to optimize a shape of the funnel 5, a shape of the funnel 5 will be described with reference to FIGS. 2A and 2B.
FIGS. 2A and 2B illustrate a stress occurred around the TOR (top of round) 7 at which the sealing surface, the body portion 51 and the yoke portion 52 of the yoke portion 52 meet, before anything else, principal factors in determining a funnel shape will be described.
In more detail, a length of an evaluation line 21 connecting the outer end of the sealing surface 4 at which the panel 1 meets the funnel 5 with the outer end of the TOR 7 at which the body portion 52 meet the yoke portion 52 is defined as b. A length from a point on the evaluation line 21, which meets a vertical line 22 having a maximum length from the outer surface of the funnel 5 to the evaluation line 21, to the outer end of the sealing surface 4 is defined as a. And, a maximum length of the vertical line 22 is defined as H.
As depicted in FIG. 2A, in the funnel shape such as FIG. 2 (hereinafter, it is referred to as A type), because an a value and a H value was relatively small, stress around the yoke portion 52 of the funnel 5 was dispersed.
However, in the A type, in the vacuum state after combining the funnel 5 with the panel 1, stress concentration not less than 12 MPa occurred on the sealing surface 4.
In more detail, in the A type funnel, as depicted in FIG. 2A, when a maximum stress on a funnel minor axis was measured, a maximum stress around the yoke portion 52 was 6.3 MPa, however, a maximum stress on the sealing surface 4 was 15.3 MPa.
In the meantime, as depicted in FIG. 2B, in the funnel shape such as FIG. 2B (hereinafter, it is referred to as B type), because an a value and a H value were relatively big, stress around the sealing surface 4 of the funnel 5 was dispersed.
However, in the B type, stress concentration not less than 12 MPa occurred around the TOR 7 at which the body portion 51 met the yoke portion 52.
In more detail, in the B type funnel shape, as depicted in FIG. 2B, when a maximum stress of the funnel minor axis was measured, a maximum stress on the central portion of the sealing surface was 11.5 MPa, however, a maximum stress around the yoke portion was 21.1 MPa.
The stress concentration occurred in the A type and B type funnels may cause breakage with crack in fabrication of the cathode ray tube, and accordingly an yield rate may be lowered.
Accordingly, it is required to research a measure which is capable of lowering stress concentration and securing impact resistance of the funnel by grasping stress dispersion tendency according to the funnel shape.
In order to solve the above-mentioned problem, in order to lower stress concentration occurred according to sliming-down of a funnel, it is an object of the present invention to provide a funnel structure for a cathode ray tube which is capable of reducing cracked inferior products in fabrication and improving an yield rate by changing a shape of a funnel without increasing a thickness thereof.
In order to achieve the above-mentioned object, in a cathode ray tube including a panel having a fluorescent surface coated onto the internal surface and a funnel comprising of a body portion connected to the panel, a yoke portion at which a deflection yoke is installed and a neck portion at which an electron gun is installed, a funnel structure for a cathode ray tube satisfies following equations 0.33xe2x89xa6Rhmaj/Rmajxe2x89xa60.51, Rhmaj=Hmaj/Umaj, Rmaj=amaj/bmaj, wherein a length of a major axis evaluation line as an imaginary line connecting the major axis outer end of a sealing surface, at which a panel meets a funnel, with the major axis outer end of a TOR (top of round), at which a body portion meets a yoke portion, is defined as bmaj; a length from a point on the major axis evaluation line, which has a maximum vertical line length to the outer surface of the funnel, to the major axis outer end of the sealing surface is defined as amaj; a maximum length of the vertical line is defined as Hmaj; and xc2xd of a major axis length of an effective surface of the panel is defined as Umaj.